This fixes a regression caused by 9c50216c7b
when the Image specified fillMode: aspectRatioCrop/Fit.
[ChangeLog][QtQuick][Image] Item::grabToImage on an Image element will now work
regardless of the Image's sourceSize or cache properties.
Change-Id: I225854c48f0c35a3cb2ef0dd56bf51bd88c31779
Reviewed-by: Robin Burchell <robin.burchell@crimson.no>